Abstract

We have carried out a comparative functional analysis of the rat $TGF-\beta 1$ and Xenopus laevis $TGF-\beta 5$ promoters across several mammalian and amphibian cell lines. Progressive deletion constructs of both the promoters have been made using a PCR based approach and the basal promoter activities studied in Xenopus tadpole cell line (XTC), Xenopus adult kidney fibroblast cell line (A6), human hepatoma cell line (HepG2), normal rat kidney cell line (NRK), and Chinese hamster ovary cell line (CHO). Data suggests that the basal promoter activity of $TGF-\beta 1$ is low as compared to $TGF-\beta 5$ promoter in XTC cells but comparable in A6 cells, while $TGF-\beta 5$ promoter shows nearly negligible activity as compared to TGF-beta5 promoter in all the tested mammalian cell lines. Moreover, $TGF-\beta 5$ promoter is found to be repressed in XTC cells on treatment with $TGF-\beta 5$ protein. Thus, the regulation of $TGF-\beta 1$ and $TGF-\beta 5$ promoters is distinct in amphibian and mammalian species. We therefore suggest that contrary to the suggested functional equivalence of $TGF-\beta 1$ and $TGF-\beta 5$ proteins, $TGF-\beta 1$ and $TGF-\beta 5$ genes have distinct functions in their respective species.